Cousinly mismatches

It’s DNA Sunday here at The Legal Genealogist and I find myself convinced, as usual, that autosomal DNA testing — atDNA for short, the kind of testing called Family Finder by Family Tree DNA and Relative Finder by 23andMe — as the King in The King and I says, “Is a puzzlement!”1

We’ve tested a fair number of people, both in our immediate family and more distant cousins out to the second cousin level. Among the closest ones tested are my Uncle David (my mother’s younger brother), my first cousin Paula (daughter of David’s and my mother’s youngest sister) and, of course, yours truly — the self-professed DNA geek who’s never met a DNA test I wouldn’t take (and hasn’t yet taken all the ones I’d like to take nor tested all the family members I’d like to test!).

The results can be A Puzzlement indeed. I was looking at them yesterday, and particularly at our matches in common, and realized that Paula and I share a total of 20 matches with our Uncle David. Of those, six are members of our Family Finder group whose tests we arranged. They represent a ton of our various lines:

• two share our Robertson-Gentry lines;
• one shares a bunch of lines — Fore, Cottrell, Buchanan, Baker, and Johnson are the closest;
• one should be only a match to our Fore line — one where we don’t know the wife’s maiden name;
• one is only in our Battles-Shew-Brewer lines; and
• one shares the Battles-Shew-Brewer lines and the Robertson-Gentry lines.

But we have 90 people — four and a half times as many as we share — that one of us matches with David — and the other one doesn’t. I have 54 matches in common with our uncle that my first cousin doesn’t share; Paula has 36 that I don’t share.

Now you might be thinking that perhaps the matches in common are really not on our mothers’ side but rather matches that might be influenced by our respective paternal lines. Say, for example, somebody who was far enough away in generations to match David but not me on my mother’s side, and then matched me through a common ancestor on my father’s side. Nice theory, except that my mother’s family has been in the United States since, oh, roughly back when God was in short pants, and my father’s family arrived in the United States in 1925.

If we were going to see that sort of accidental common matching, it’d be in Paula’s matches that we might actually expect it — someone who’s far enough away in generations to match David but not Paula and who then shares enough DNA with Paula’s father to show up as a match to her as well. Her Dad’s family has been in America probably as long as our joint mothers’ family has.

But we don’t see it there at all. I have nearly twice as many matches in common with David as Paula does. David and I share matches with many many more of our Gentry relatives; Paula matches more in what we think will be the Fore-Johnson line. And we wonder why; we wonder if there even could be a reason why, given the randomness of recombination.2 Why did more of my genes come from the same batch that our uncle got, and fewer of my cousin’s genes?

The only thing that seems different between us is our places in our family. My mother was in the first half of her generational birth order, my grandparents’ fifth-born and fourth-surviving child; Paula’s mother was their 12th-born and last of 10 surviving children. (David is the sixth-born and fifth-surviving child.) And I’m way up in the top end of my generation (third of all the cousins) and Paula is next to the youngest. Could it be that birth order played some role in who got what genes?

Probably not,3 but hey… it’s as good a theory as any, and trying it on for size gives me the excuse to round up more family members to test.

Yep, I took advantage of the Family Tree DNA sale yesterday and ordered two more test kits: one for the oldest surviving Cottrell child (other than David), our Aunt Carol; and one for the youngest surviving child (other than Paula’s mother), our Uncle Mike.

If nothing else, it’ll give us more information on our grandparents’ genomes. And that’s not a bad thing at all.

6 Responses to Cousinly mismatches

Judy, birth order has interesting influences in many ways, but I’m pretty certain that one’s various siblings didn’t influence one’s DNA IMHO. Although I blame them for lots of things! I’m open to the possibility, as I toss my curly hair (from paternal grandmother line), blink my blue eyes (from maternal line), and stretch my back (above-average height from maternal father’s line)… And think of my 4 adult kids. When we get enough tests done, there will be wonderful matches, I’m sure. Cheers on a very interesting post, more education for us all on DNA.

My husband and I do not match DNA. I entered both of our data on GEDMATCH.com. Then I finally convinced MY first cousin to test and of course we match quite well.

So finally since some time had passed I decided to check my husband’s matches again. But I kept getting his top match as my cousin and I knew that couldn’t be right so I checked and checked and re-checked the numbers and my husband’s top match is my first cousin!!!! And my children match my first cousin on segments we share and on the segments my husband shares. We cannot find the connection and the families lived 3,000 miles apart. However they both go back to New England and Scandinavia. That blew my socks off!

Thanks for the kind words, Kelly — and oh yeah… those cousins matching cousins issues can sure be fun! My cousin Paula and I practically fell off our chairs laughing when one of her father’s top matches turned out to be our fifth cousin on our mothers’ side!

The autosomal testing has raised so many questions for our family. My parents do not match, but they have several matches in common, including a known cousin on my father’s side. I am still trying to figure out the connections.

Jody, if both of your parents have US ancestry back aways, then frankly it’d be surprising for them NOT to have matches in common. One reason is a concept called pedigree collapse or family tree collapse. Think about it: you have two parents, four grandparents, eight great grandparents and so on back through time. Pretty soon, you have more ancestors numerically than ever lived on earth! In reality, we all descend from many fewer people than there are slots on our family trees, and many of those marriages were between cousins. (I saw an article last year where a Rutgers University prof estimated that as many as 80 percent of all marriages in early years were between cousins.) What the results suggest is that your parents are not themselves closely related but they may very well have had ancestors in common many generations back.